I have 2 55 gallon drums stored away in my garage. I use $14 water preserver from amazon. Its slowly releases the bleach over 5 years. The trick is you have to quickly seal the barrel and never open until an emergency or after 5 years when its time to rotate. The intraweb says to keep out of sunlight and never place ontop of cemented floors. The cement can leach chemicals up into your plastic barrel. To be safe I built a small platform and place them ontop of it. This is my first time using the Water Preserver I wont know if it worked until 2017. Good Luck
Be fit everyday.